A server thread associated with your session has been suspended, most likely because of a serious internal error. Evidence about the problem has been gathered and written to an Assertion Failure file, and your online log should contain more information.
Before suspending the session thread, the server attempted to roll back all work performed by the current transaction. Your connection to the server might also have been broken, depending on the type of thread that was suspended. At a minimum, you will have to begin a new transaction.
Contact IBM Informix Technical Support and provide them with your Assertion Failure file.